The present invention relates in general to sewing machines and in particular to a new and useful sewing machine having a spooling mechanism for winding a spool of thread, the sewing machine having an armshaft connected to a hand wheel by a coupling, and a pulse generator associated with the armshaft for generating pulses corresponding to the speed of the armshaft.
While switching a sewing machine of this kind to spooling, the armshaft and thereby the entire sewing mechanism becomes uncoupled from the sewing motor. The pulse generator coupled to the armshaft is then also uncoupled and no pulses are delivered to the control device of the sewing motor.
A prior art sewing machine therefore comprises a microswitch which is actuated while switching on the spooling mechanism and by which the control device connected between the sewing motor and the control pontentiometer is short circuited. Otherwise, with the sewing mechanism stopped, too low a speed of the sewing motor would be detected and the control device would unduly increase the speed.
This arrangement has the disadvantage that no spooling is possible during a sewing operation. Even with a mistaken switching to spooling during a sewing operation, the sewing motor is under control operation and only a very small piercing force of the needle is obtained and no positioning of the needle is possible.